Planetary gear trains are supplied with a suitable lubricant such as oil to reduce friction and provide wear protection for gear teeth, bearing surfaces, and other contacting surfaces in relative motion. The lubricant is also a medium for conducting waste heat away from the gear train.
In typical prior art gear trains, once the oil is spent, i.e. has lubricated and cooled the gear train, gravity causes the oil to drain into a sump below the bottom of the gear train. Oil that collects in the sump is pumped through the lubrication system coolers, filters and deaerators to be reconditioned for continual use.
Such passive collection of the spent oil does not lend itself to rapid removal of oil from the gear train. Spent oil which remains in the gear system adds to the fluid drag or windage against the moving surfaces and also reenters the gear meshes where it is agitated by the gear teeth. This results in high parasitic power losses and higher oil temperature than would be experienced if the spent oil were rapidly removed. Moreover, since spent oil is not cooled until it is removed from the gear train and made available to the lubrication system heat exchangers, the retention of spent oil in the gear system causes ineffective heat transfer out of the oil.
Because of the accumulation of oil in the gear train, the lubrication system contains a greater volume of oil than it would if the oil were rapidly removed and recirculated through the system. This is a disadvantage in applications such as aircraft where weight and compactness are important.
Therefore, it is seen that the traditional passive approach of removing the spent oil by draining it into a sump contributes to parasitic power losses, introduces heat transfer inefficiencies and contributes undesirable weight and bulk to the lubrication system. In view of these shortcomings, an oil recovery system that reduces parasitic power losses and enhances heat transfer by rapidly removing the spent oil is sought.